[PATCH 10/11] acpi: Export acpi_bus_type

[PATCH 10/11] acpi: Export acpi_bus_type

[ankitprasad.r.sharma]

From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>

Some modules, like i915.ko, needs to detect when certain ACPI features
are active inorder to prevent corruption on contended resources.
In particular, use of BIOS RapidStart Technology may corrupt the contents
of the reserved graphics memory, due to unalarmed hibernation. In which
case i915.ko cannot assume that it (reserved gfx memory) remains
unmodified and must recreate teh contents and importantly not use it to
store unrecoverable user data.

Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Len Brown <lenb@kernel.org>
Cc: linux-acpi@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/acpi/bus.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index a212cef..69509c7 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
 	.remove		= acpi_device_remove,
 	.uevent		= acpi_device_uevent,
 };
+EXPORT_SYMBOL_GPL(acpi_bus_type);
 
 /* --------------------------------------------------------------------------
                              Initialization/Cleanup
-- 
1.9.1

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Rafael J. Wysocki]

On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> 
> Some modules, like i915.ko, needs to detect when certain ACPI features
> are active inorder to prevent corruption on contended resources.
> In particular, use of BIOS RapidStart Technology may corrupt the contents
> of the reserved graphics memory, due to unalarmed hibernation. In which
> case i915.ko cannot assume that it (reserved gfx memory) remains
> unmodified and must recreate teh contents and importantly not use it to
> store unrecoverable user data.
> 
> Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Len Brown <lenb@kernel.org>
> Cc: linux-acpi@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
>  drivers/acpi/bus.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> index a212cef..69509c7 100644
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
>  	.remove		= acpi_device_remove,
>  	.uevent		= acpi_device_uevent,
>  };
> +EXPORT_SYMBOL_GPL(acpi_bus_type);
>  
>  /* --------------------------------------------------------------------------
>                               Initialization/Cleanup
> 

No.

I see no reason whatsoever for doing this.

Thanks,
Rafael

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Ankitprasad Sharma]

On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> > From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > 
> > Some modules, like i915.ko, needs to detect when certain ACPI features
> > are active inorder to prevent corruption on contended resources.
> > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > of the reserved graphics memory, due to unalarmed hibernation. In which
> > case i915.ko cannot assume that it (reserved gfx memory) remains
> > unmodified and must recreate teh contents and importantly not use it to
> > store unrecoverable user data.
> > 
> > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > Cc: Len Brown <lenb@kernel.org>
> > Cc: linux-acpi@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > ---
> >  drivers/acpi/bus.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > index a212cef..69509c7 100644
> > --- a/drivers/acpi/bus.c
> > +++ b/drivers/acpi/bus.c
> > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> >  	.remove		= acpi_device_remove,
> >  	.uevent		= acpi_device_uevent,
> >  };
> > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> >  
> >  /* --------------------------------------------------------------------------
> >                               Initialization/Cleanup
> > 
> 
> No.
> 
> I see no reason whatsoever for doing this.
> 
> Thanks,
> Rafael
Hi Rafael,

Thanks for the response.

Can you please help me with, how to detect the presence of a certain
acpi device using its id (for example, INT3392 for Intel RST device)? 

As you might have seen (in the next patch in this series), that we use
this symbol (acpi_bus_type) to iterate over all the devices registered
on acpi bus, to check if there is a device with id INT3392 present or
not.

Thanks,
Ankit

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Rafael J. Wysocki]

On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:
> On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> > On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> > > From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > 
> > > Some modules, like i915.ko, needs to detect when certain ACPI features
> > > are active inorder to prevent corruption on contended resources.
> > > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > > of the reserved graphics memory, due to unalarmed hibernation. In which
> > > case i915.ko cannot assume that it (reserved gfx memory) remains
> > > unmodified and must recreate teh contents and importantly not use it to
> > > store unrecoverable user data.
> > > 
> > > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > > Cc: Len Brown <lenb@kernel.org>
> > > Cc: linux-acpi@vger.kernel.org
> > > Cc: linux-kernel@vger.kernel.org
> > > ---
> > >  drivers/acpi/bus.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > > index a212cef..69509c7 100644
> > > --- a/drivers/acpi/bus.c
> > > +++ b/drivers/acpi/bus.c
> > > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> > >  	.remove		= acpi_device_remove,
> > >  	.uevent		= acpi_device_uevent,
> > >  };
> > > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> > >  
> > >  /* --------------------------------------------------------------------------
> > >                               Initialization/Cleanup
> > > 
> > 
> > No.
> > 
> > I see no reason whatsoever for doing this.
> > 
> > Thanks,
> > Rafael
> Hi Rafael,
> 
> Thanks for the response.
> 
> Can you please help me with, how to detect the presence of a certain
> acpi device using its id (for example, INT3392 for Intel RST device)? 

If you want to check if the device ir present at all, you cen use
acpi_device_is_present() introduced recently (although that would need
to be exported if you want to use it from a driver).

> As you might have seen (in the next patch in this series), that we use
> this symbol (acpi_bus_type) to iterate over all the devices registered
> on acpi bus, to check if there is a device with id INT3392 present or
> not.

Please don't do that this way.

I'll have a look at the other patch later.

Thanks,
Rafael

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Lukas Wunner]

Hi,

On Mon, Jan 18, 2016 at 03:57:29PM +0100, Rafael J. Wysocki wrote:
> On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:
> > On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> > > On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> > > > From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > 
> > > > Some modules, like i915.ko, needs to detect when certain ACPI features
> > > > are active inorder to prevent corruption on contended resources.
> > > > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > > > of the reserved graphics memory, due to unalarmed hibernation. In which
> > > > case i915.ko cannot assume that it (reserved gfx memory) remains
> > > > unmodified and must recreate teh contents and importantly not use it to
> > > > store unrecoverable user data.
> > > > 
> > > > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > > > Cc: Len Brown <lenb@kernel.org>
> > > > Cc: linux-acpi@vger.kernel.org
> > > > Cc: linux-kernel@vger.kernel.org
> > > > ---
> > > >  drivers/acpi/bus.c | 1 +
> > > >  1 file changed, 1 insertion(+)
> > > > 
> > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > > > index a212cef..69509c7 100644
> > > > --- a/drivers/acpi/bus.c
> > > > +++ b/drivers/acpi/bus.c
> > > > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> > > >  	.remove		= acpi_device_remove,
> > > >  	.uevent		= acpi_device_uevent,
> > > >  };
> > > > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> > > >  
> > > >  /* --------------------------------------------------------------------------
> > > >                               Initialization/Cleanup
> > > > 
> > > 
> > > No.
> > > 
> > > I see no reason whatsoever for doing this.
> > > 
> > > Thanks,
> > > Rafael
> > Hi Rafael,
> > 
> > Thanks for the response.
> > 
> > Can you please help me with, how to detect the presence of a certain
> > acpi device using its id (for example, INT3392 for Intel RST device)? 
> 
> If you want to check if the device ir present at all, you cen use
> acpi_device_is_present() introduced recently (although that would need
> to be exported if you want to use it from a driver).

acpi_dev_present() is exported, so can be used in drivers just fine:
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=2d12b6b381ba059d5f92798f5ea739672a2f5fcf


> > As you might have seen (in the next patch in this series), that we use
> > this symbol (acpi_bus_type) to iterate over all the devices registered
> > on acpi bus, to check if there is a device with id INT3392 present or
> > not.

Ankitprasad, just change your patch [11/11] thusly:

-       if (intel_detect_acpi_rst()) {
+       if (acpi_dev_present("INT3392")) {


Using bus_for_each_dev() was the wrong approach, most drivers call
acpi_get_devices() to detect the presence of a particular HID,
however that necessitates the definition of a callback in each driver,
leading to lots of duplicate code. Hence the introduction of
acpi_dev_present() which is also faster because it just iterates over
a list instead of walking the namespace.

This new API landed in Linus' tree last Tuesday (PST), so you need
to merge Linus' tree back into yours or wait until it gets merged
into drm-intel-nightly.

Best regards,

Lukas

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Ankitprasad Sharma]

On Mon, 2016-01-18 at 19:26 +0100, Lukas Wunner wrote:
Hi,
> Hi,
> 
> On Mon, Jan 18, 2016 at 03:57:29PM +0100, Rafael J. Wysocki wrote:
> > On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:
> > > On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> > > > On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> > > > > From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > > 
> > > > > Some modules, like i915.ko, needs to detect when certain ACPI features
> > > > > are active inorder to prevent corruption on contended resources.
> > > > > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > > > > of the reserved graphics memory, due to unalarmed hibernation. In which
> > > > > case i915.ko cannot assume that it (reserved gfx memory) remains
> > > > > unmodified and must recreate teh contents and importantly not use it to
> > > > > store unrecoverable user data.
> > > > > 
> > > > > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > > > > Cc: Len Brown <lenb@kernel.org>
> > > > > Cc: linux-acpi@vger.kernel.org
> > > > > Cc: linux-kernel@vger.kernel.org
> > > > > ---
> > > > >  drivers/acpi/bus.c | 1 +
> > > > >  1 file changed, 1 insertion(+)
> > > > > 
> > > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > > > > index a212cef..69509c7 100644
> > > > > --- a/drivers/acpi/bus.c
> > > > > +++ b/drivers/acpi/bus.c
> > > > > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> > > > >  	.remove		= acpi_device_remove,
> > > > >  	.uevent		= acpi_device_uevent,
> > > > >  };
> > > > > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> > > > >  
> > > > >  /* --------------------------------------------------------------------------
> > > > >                               Initialization/Cleanup
> > > > > 
> > > > 
> > > > No.
> > > > 
> > > > I see no reason whatsoever for doing this.
> > > > 
> > > > Thanks,
> > > > Rafael
> > > Hi Rafael,
> > > 
> > > Thanks for the response.
> > > 
> > > Can you please help me with, how to detect the presence of a certain
> > > acpi device using its id (for example, INT3392 for Intel RST device)? 
> > 
> > If you want to check if the device ir present at all, you cen use
> > acpi_device_is_present() introduced recently (although that would need
> > to be exported if you want to use it from a driver).
> 
> acpi_dev_present() is exported, so can be used in drivers just fine:
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=2d12b6b381ba059d5f92798f5ea739672a2f5fcf
> 
> 
> > > As you might have seen (in the next patch in this series), that we use
> > > this symbol (acpi_bus_type) to iterate over all the devices registered
> > > on acpi bus, to check if there is a device with id INT3392 present or
> > > not.
> 
> Ankitprasad, just change your patch [11/11] thusly:
> 
> -       if (intel_detect_acpi_rst()) {
> +       if (acpi_dev_present("INT3392")) {
> 
> 
> Using bus_for_each_dev() was the wrong approach, most drivers call
> acpi_get_devices() to detect the presence of a particular HID,
> however that necessitates the definition of a callback in each driver,
> leading to lots of duplicate code. Hence the introduction of
> acpi_dev_present() which is also faster because it just iterates over
> a list instead of walking the namespace.
> 
> This new API landed in Linus' tree last Tuesday (PST), so you need
> to merge Linus' tree back into yours or wait until it gets merged
> into drm-intel-nightly.
> 
> Best regards,
> 
> Lukas

Thank you, Lukas/Rafael.

-Ankit

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Rafael J. Wysocki]

On Monday, January 18, 2016 03:57:29 PM Rafael J. Wysocki wrote:
> On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:
> > On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> > > On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> > > > From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > 
> > > > Some modules, like i915.ko, needs to detect when certain ACPI features
> > > > are active inorder to prevent corruption on contended resources.
> > > > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > > > of the reserved graphics memory, due to unalarmed hibernation. In which
> > > > case i915.ko cannot assume that it (reserved gfx memory) remains
> > > > unmodified and must recreate teh contents and importantly not use it to
> > > > store unrecoverable user data.
> > > > 
> > > > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > > > Cc: Len Brown <lenb@kernel.org>
> > > > Cc: linux-acpi@vger.kernel.org
> > > > Cc: linux-kernel@vger.kernel.org
> > > > ---
> > > >  drivers/acpi/bus.c | 1 +
> > > >  1 file changed, 1 insertion(+)
> > > > 
> > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > > > index a212cef..69509c7 100644
> > > > --- a/drivers/acpi/bus.c
> > > > +++ b/drivers/acpi/bus.c
> > > > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> > > >  	.remove		= acpi_device_remove,
> > > >  	.uevent		= acpi_device_uevent,
> > > >  };
> > > > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> > > >  
> > > >  /* --------------------------------------------------------------------------
> > > >                               Initialization/Cleanup
> > > > 
> > > 
> > > No.
> > > 
> > > I see no reason whatsoever for doing this.
> > > 
> > > Thanks,
> > > Rafael
> > Hi Rafael,
> > 
> > Thanks for the response.
> > 
> > Can you please help me with, how to detect the presence of a certain
> > acpi device using its id (for example, INT3392 for Intel RST device)? 
> 
> If you want to check if the device ir present at all, you cen use
> acpi_device_is_present() introduced recently (although that would need
> to be exported if you want to use it from a driver).

I meant acpi_dev_present(), sorry about the mistake.

I guess we should rename it to acpi_device_found() or something similar
to avoid such confusion in the future.

Thanks,
Rafael

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Lukas Wunner]

Hi,

On Mon, Jan 18, 2016 at 11:28:27PM +0100, Rafael J. Wysocki wrote:
> On Monday, January 18, 2016 03:57:29 PM Rafael J. Wysocki wrote:
> > On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:
> > > On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> > > > On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> > > > > From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > > 
> > > > > Some modules, like i915.ko, needs to detect when certain ACPI features
> > > > > are active inorder to prevent corruption on contended resources.
> > > > > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > > > > of the reserved graphics memory, due to unalarmed hibernation. In which
> > > > > case i915.ko cannot assume that it (reserved gfx memory) remains
> > > > > unmodified and must recreate teh contents and importantly not use it to
> > > > > store unrecoverable user data.
> > > > > 
> > > > > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > > > > Cc: Len Brown <lenb@kernel.org>
> > > > > Cc: linux-acpi@vger.kernel.org
> > > > > Cc: linux-kernel@vger.kernel.org
> > > > > ---
> > > > >  drivers/acpi/bus.c | 1 +
> > > > >  1 file changed, 1 insertion(+)
> > > > > 
> > > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > > > > index a212cef..69509c7 100644
> > > > > --- a/drivers/acpi/bus.c
> > > > > +++ b/drivers/acpi/bus.c
> > > > > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> > > > >  	.remove		= acpi_device_remove,
> > > > >  	.uevent		= acpi_device_uevent,
> > > > >  };
> > > > > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> > > > >  
> > > > >  /* --------------------------------------------------------------------------
> > > > >                               Initialization/Cleanup
> > > > > 
> > > > 
> > > > No.
> > > > 
> > > > I see no reason whatsoever for doing this.
> > > > 
> > > > Thanks,
> > > > Rafael
> > > Hi Rafael,
> > > 
> > > Thanks for the response.
> > > 
> > > Can you please help me with, how to detect the presence of a certain
> > > acpi device using its id (for example, INT3392 for Intel RST device)? 
> > 
> > If you want to check if the device ir present at all, you cen use
> > acpi_device_is_present() introduced recently (although that would need
> > to be exported if you want to use it from a driver).
> 
> I meant acpi_dev_present(), sorry about the mistake.
> 
> I guess we should rename it to acpi_device_found() or something similar
> to avoid such confusion in the future.

The name was chosen because the PCI equivalent is called pci_dev_present()
and I assumed that name already stuck in developers' heads, so if they're
looking for an ACPI presence detection function, that's what they'd look
for first.

Best regards,

Lukas

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Rafael J. Wysocki]

On Monday, January 18, 2016 11:39:07 PM Lukas Wunner wrote:
> Hi,
> 
> On Mon, Jan 18, 2016 at 11:28:27PM +0100, Rafael J. Wysocki wrote:
> > On Monday, January 18, 2016 03:57:29 PM Rafael J. Wysocki wrote:
> > > On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:
> > > > On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> > > > > On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> > > > > > From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > > > 
> > > > > > Some modules, like i915.ko, needs to detect when certain ACPI features
> > > > > > are active inorder to prevent corruption on contended resources.
> > > > > > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > > > > > of the reserved graphics memory, due to unalarmed hibernation. In which
> > > > > > case i915.ko cannot assume that it (reserved gfx memory) remains
> > > > > > unmodified and must recreate teh contents and importantly not use it to
> > > > > > store unrecoverable user data.
> > > > > > 
> > > > > > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > > > > > Cc: Len Brown <lenb@kernel.org>
> > > > > > Cc: linux-acpi@vger.kernel.org
> > > > > > Cc: linux-kernel@vger.kernel.org
> > > > > > ---
> > > > > >  drivers/acpi/bus.c | 1 +
> > > > > >  1 file changed, 1 insertion(+)
> > > > > > 
> > > > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > > > > > index a212cef..69509c7 100644
> > > > > > --- a/drivers/acpi/bus.c
> > > > > > +++ b/drivers/acpi/bus.c
> > > > > > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> > > > > >  	.remove		= acpi_device_remove,
> > > > > >  	.uevent		= acpi_device_uevent,
> > > > > >  };
> > > > > > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> > > > > >  
> > > > > >  /* --------------------------------------------------------------------------
> > > > > >                               Initialization/Cleanup
> > > > > > 
> > > > > 
> > > > > No.
> > > > > 
> > > > > I see no reason whatsoever for doing this.
> > > > > 
> > > > > Thanks,
> > > > > Rafael
> > > > Hi Rafael,
> > > > 
> > > > Thanks for the response.
> > > > 
> > > > Can you please help me with, how to detect the presence of a certain
> > > > acpi device using its id (for example, INT3392 for Intel RST device)? 
> > > 
> > > If you want to check if the device ir present at all, you cen use
> > > acpi_device_is_present() introduced recently (although that would need
> > > to be exported if you want to use it from a driver).
> > 
> > I meant acpi_dev_present(), sorry about the mistake.
> > 
> > I guess we should rename it to acpi_device_found() or something similar
> > to avoid such confusion in the future.
> 
> The name was chosen because the PCI equivalent is called pci_dev_present()
> and I assumed that name already stuck in developers' heads, so if they're
> looking for an ACPI presence detection function, that's what they'd look
> for first.

But "present" in ACPI really means something different.  There may be ACPI
device objects in the namespace for devices that are not *actually* present.

Thanks,
Rafael

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Lukas Wunner]

Hi,

On Mon, Jan 18, 2016 at 11:46:18PM +0100, Rafael J. Wysocki wrote:
> On Monday, January 18, 2016 11:39:07 PM Lukas Wunner wrote:
> > Hi,
> > 
> > On Mon, Jan 18, 2016 at 11:28:27PM +0100, Rafael J. Wysocki wrote:
> > > On Monday, January 18, 2016 03:57:29 PM Rafael J. Wysocki wrote:
> > > > On Monday, January 18, 2016 02:31:00 PM Ankitprasad Sharma wrote:
> > > > > On Fri, 2016-01-15 at 15:51 +0100, Rafael J. Wysocki wrote:
> > > > > > On Thursday, January 14, 2016 11:46:46 AM ankitprasad.r.sharma@intel.com wrote:
> > > > > > > From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > > > > 
> > > > > > > Some modules, like i915.ko, needs to detect when certain ACPI features
> > > > > > > are active inorder to prevent corruption on contended resources.
> > > > > > > In particular, use of BIOS RapidStart Technology may corrupt the contents
> > > > > > > of the reserved graphics memory, due to unalarmed hibernation. In which
> > > > > > > case i915.ko cannot assume that it (reserved gfx memory) remains
> > > > > > > unmodified and must recreate teh contents and importantly not use it to
> > > > > > > store unrecoverable user data.
> > > > > > > 
> > > > > > > Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> > > > > > > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > > > > > > Cc: Len Brown <lenb@kernel.org>
> > > > > > > Cc: linux-acpi@vger.kernel.org
> > > > > > > Cc: linux-kernel@vger.kernel.org
> > > > > > > ---
> > > > > > >  drivers/acpi/bus.c | 1 +
> > > > > > >  1 file changed, 1 insertion(+)
> > > > > > > 
> > > > > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > > > > > > index a212cef..69509c7 100644
> > > > > > > --- a/drivers/acpi/bus.c
> > > > > > > +++ b/drivers/acpi/bus.c
> > > > > > > @@ -814,6 +814,7 @@ struct bus_type acpi_bus_type = {
> > > > > > >  	.remove		= acpi_device_remove,
> > > > > > >  	.uevent		= acpi_device_uevent,
> > > > > > >  };
> > > > > > > +EXPORT_SYMBOL_GPL(acpi_bus_type);
> > > > > > >  
> > > > > > >  /* --------------------------------------------------------------------------
> > > > > > >                               Initialization/Cleanup
> > > > > > > 
> > > > > > 
> > > > > > No.
> > > > > > 
> > > > > > I see no reason whatsoever for doing this.
> > > > > > 
> > > > > > Thanks,
> > > > > > Rafael
> > > > > Hi Rafael,
> > > > > 
> > > > > Thanks for the response.
> > > > > 
> > > > > Can you please help me with, how to detect the presence of a certain
> > > > > acpi device using its id (for example, INT3392 for Intel RST device)?
> > > > 
> > > > If you want to check if the device ir present at all, you cen use
> > > > acpi_device_is_present() introduced recently (although that would need
> > > > to be exported if you want to use it from a driver).
> > > 
> > > I meant acpi_dev_present(), sorry about the mistake.
> > > 
> > > I guess we should rename it to acpi_device_found() or something similar
> > > to avoid such confusion in the future.
> > 
> > The name was chosen because the PCI equivalent is called pci_dev_present()
> > and I assumed that name already stuck in developers' heads, so if they're
> > looking for an ACPI presence detection function, that's what they'd look
> > for first.
> 
> But "present" in ACPI really means something different.  There may be ACPI
> device objects in the namespace for devices that are not *actually* present.

You mean synthesized devices like LNXSYBUS?
Don't think anyone is going to test for the presence of that.

I've posted 5 patches over the last days which use acpi_dev_present():

http://lists.freedesktop.org/archives/dri-devel/2016-January/098403.html
http://mailman.alsa-project.org/pipermail/alsa-devel/2016-January/103056.html
http://mailman.alsa-project.org/pipermail/alsa-devel/2016-January/103058.html
http://thread.gmane.org/gmane.linux.drivers.platform.x86.devel/8474/focus=8475
http://thread.gmane.org/gmane.linux.drivers.platform.x86.devel/8474/focus=8476

When considering a rename of the function, please bear in mind that it
will cause breakage for anyone testing or merging these patches.
(Postponing a rename until these patches have landed would avoid that.)

Thanks,

Lukas

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Rafael J. Wysocki]

On Tuesday, January 19, 2016 12:00:47 AM Lukas Wunner wrote:
> Hi,
> 
> On Mon, Jan 18, 2016 at 11:46:18PM +0100, Rafael J. Wysocki wrote:
> > On Monday, January 18, 2016 11:39:07 PM Lukas Wunner wrote:

[cut]

> > > > > If you want to check if the device ir present at all, you cen use
> > > > > acpi_device_is_present() introduced recently (although that would need
> > > > > to be exported if you want to use it from a driver).
> > > > 
> > > > I meant acpi_dev_present(), sorry about the mistake.
> > > > 
> > > > I guess we should rename it to acpi_device_found() or something similar
> > > > to avoid such confusion in the future.
> > > 
> > > The name was chosen because the PCI equivalent is called pci_dev_present()
> > > and I assumed that name already stuck in developers' heads, so if they're
> > > looking for an ACPI presence detection function, that's what they'd look
> > > for first.
> > 
> > But "present" in ACPI really means something different.  There may be ACPI
> > device objects in the namespace for devices that are not *actually* present.
> 
> You mean synthesized devices like LNXSYBUS?
> Don't think anyone is going to test for the presence of that.

No, I mean real devices, where the corresponding ACPI object has _STA that
returns 0.

There may be a couple of reasons for that.  The device the ACPI object
corresponds to may not be physically present (eg. it may possible to
hot-add it) or the device may depend on something else for functionality
and that thing hasn't been set up yet etc.

The presence of an ACPI device object in the namespace means that the
platform firmware knows about the device, but it need not mean that
the device is really there.  _STA returns that piece of information.

> 
> I've posted 5 patches over the last days which use acpi_dev_present():
> 
> http://lists.freedesktop.org/archives/dri-devel/2016-January/098403.html
> http://mailman.alsa-project.org/pipermail/alsa-devel/2016-January/103056.html
> http://mailman.alsa-project.org/pipermail/alsa-devel/2016-January/103058.html
> http://thread.gmane.org/gmane.linux.drivers.platform.x86.devel/8474/focus=8475
> http://thread.gmane.org/gmane.linux.drivers.platform.x86.devel/8474/focus=8476
> 
> When considering a rename of the function, please bear in mind that it
> will cause breakage for anyone testing or merging these patches.
> (Postponing a rename until these patches have landed would avoid that.)

No problem with that.  Please let me know when these patches are merged.

Thanks,
Rafael

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Lukas Wunner]

Hi Rafael,

On Tue, Jan 19, 2016 at 12:59:13AM +0100, Rafael J. Wysocki wrote:
> On Tuesday, January 19, 2016 12:00:47 AM Lukas Wunner wrote:
> > Hi,
> > 
> > On Mon, Jan 18, 2016 at 11:46:18PM +0100, Rafael J. Wysocki wrote:
> > > On Monday, January 18, 2016 11:39:07 PM Lukas Wunner wrote:
> 
> [cut]
> 
> > > > > > If you want to check if the device ir present at all, you cen use
> > > > > > acpi_device_is_present() introduced recently (although that would need
> > > > > > to be exported if you want to use it from a driver).
> > > > > 
> > > > > I meant acpi_dev_present(), sorry about the mistake.
> > > > > 
> > > > > I guess we should rename it to acpi_device_found() or something similar
> > > > > to avoid such confusion in the future.
> > > > 
> > > > The name was chosen because the PCI equivalent is called pci_dev_present()
> > > > and I assumed that name already stuck in developers' heads, so if they're
> > > > looking for an ACPI presence detection function, that's what they'd look
> > > > for first.
> > > 
> > > But "present" in ACPI really means something different.  There may be ACPI
> > > device objects in the namespace for devices that are not *actually* present.
> > 
> > You mean synthesized devices like LNXSYBUS?
> > Don't think anyone is going to test for the presence of that.
> 
> No, I mean real devices, where the corresponding ACPI object has _STA that
> returns 0.
> 
> There may be a couple of reasons for that.  The device the ACPI object
> corresponds to may not be physically present (eg. it may possible to
> hot-add it) or the device may depend on something else for functionality
> and that thing hasn't been set up yet etc.
> 
> The presence of an ACPI device object in the namespace means that the
> platform firmware knows about the device, but it need not mean that
> the device is really there.  _STA returns that piece of information.

Thank you for the clarification, these are very good points.

The drivers in question use acpi_get_devices() merely to probe for
presence of a device in the namespace. They do not invoke _STA,
nor do they even hold a pointer to the acpi_device or acpi_handle
when detecting presence. Mostly this is about activating quirks
if a certain ACPI device is detected.

Currently about 50% of the calls to acpi_get_devices() in the drivers
fit this pattern and the point of acpi_dev_present() is to give
developers a simple, lightweight tool as an alternative.

However the kernel-doc should be amended to clarify that _STA is not
invoked. The patch below is a suggestion, feel free to rephrase.

Thanks & best regards,

Lukas

-- >8 --
Subject: [PATCH] ACPI / utils: Clarify appropriate usage of acpi_dev_present()

Rafael J. Wysocki pointed out that even though a device is present
in the namespace, its _STA control method might still return 0 in the
"device is present" bit. Amend the documentation accordingly.

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
 drivers/acpi/utils.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
index f2f9873..99af3bc 100644
--- a/drivers/acpi/utils.c
+++ b/drivers/acpi/utils.c
@@ -716,6 +716,8 @@ EXPORT_SYMBOL(acpi_check_dsm);
  *
  * Return %true if the device was present at the moment of invocation.
  * Note that if the device is pluggable, it may since have disappeared.
+ * Also, this merely checks presence in the namespace but does not
+ * invoke the _STA control method.
  *
  * For this function to work, acpi_bus_scan() must have been executed
  * which happens in the subsys_initcall() subsection. Hence, do not
-- 
1.8.5.2 (Apple Git-48)

Re: [PATCH 10/11] acpi: Export acpi_bus_type

[Rafael J. Wysocki]

On Tuesday, January 19, 2016 05:31:04 PM Lukas Wunner wrote:
> Hi Rafael,
> 
> On Tue, Jan 19, 2016 at 12:59:13AM +0100, Rafael J. Wysocki wrote:
> > On Tuesday, January 19, 2016 12:00:47 AM Lukas Wunner wrote:
> > > Hi,
> > > 
> > > On Mon, Jan 18, 2016 at 11:46:18PM +0100, Rafael J. Wysocki wrote:
> > > > On Monday, January 18, 2016 11:39:07 PM Lukas Wunner wrote:
> > 
> > [cut]
> > 
> > > > > > > If you want to check if the device ir present at all, you cen use
> > > > > > > acpi_device_is_present() introduced recently (although that would need
> > > > > > > to be exported if you want to use it from a driver).
> > > > > > 
> > > > > > I meant acpi_dev_present(), sorry about the mistake.
> > > > > > 
> > > > > > I guess we should rename it to acpi_device_found() or something similar
> > > > > > to avoid such confusion in the future.
> > > > > 
> > > > > The name was chosen because the PCI equivalent is called pci_dev_present()
> > > > > and I assumed that name already stuck in developers' heads, so if they're
> > > > > looking for an ACPI presence detection function, that's what they'd look
> > > > > for first.
> > > > 
> > > > But "present" in ACPI really means something different.  There may be ACPI
> > > > device objects in the namespace for devices that are not *actually* present.
> > > 
> > > You mean synthesized devices like LNXSYBUS?
> > > Don't think anyone is going to test for the presence of that.
> > 
> > No, I mean real devices, where the corresponding ACPI object has _STA that
> > returns 0.
> > 
> > There may be a couple of reasons for that.  The device the ACPI object
> > corresponds to may not be physically present (eg. it may possible to
> > hot-add it) or the device may depend on something else for functionality
> > and that thing hasn't been set up yet etc.
> > 
> > The presence of an ACPI device object in the namespace means that the
> > platform firmware knows about the device, but it need not mean that
> > the device is really there.  _STA returns that piece of information.
> 
> Thank you for the clarification, these are very good points.
> 
> The drivers in question use acpi_get_devices() merely to probe for
> presence of a device in the namespace. They do not invoke _STA,
> nor do they even hold a pointer to the acpi_device or acpi_handle
> when detecting presence. Mostly this is about activating quirks
> if a certain ACPI device is detected.

I know, but it doesn't matter too much.  I don't want people to wonder
what the difference between acpi_dev_present() and acpi_device_is_present()
is and when to use which of them.

> Currently about 50% of the calls to acpi_get_devices() in the drivers
> fit this pattern and the point of acpi_dev_present() is to give
> developers a simple, lightweight tool as an alternative.

Again, I know, but the name of the function should be different.

> However the kernel-doc should be amended to clarify that _STA is not
> invoked. The patch below is a suggestion, feel free to rephrase.

That's OK, but it's not enough.

I guess it won't be a big deal to change the function name and rebase
the patches depending on it on top of that change, will it?

Thanks,
Rafael

[PATCH 11/11] drm/i915: Disable use of stolen area by User when Intel RST is present

[ankitprasad.r.sharma]

From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>

The BIOS RapidStartTechnology may corrupt the stolen memory across S3
suspend due to unalarmed hibernation, in which case we will not be able
to preserve the User data stored in the stolen region. Hence this patch
tries to identify presence of the RST device on the ACPI bus, and
disables use of stolen memory (for persistent data) if found.

v2: Updated comment, updated/corrected new functions private to driver
(Chris/Tvrtko)

Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Len Brown <lenb@kernel.org>
Cc: linux-acpi@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/gpu/drm/i915/i915_drv.h        | 11 +++++++++++
 drivers/gpu/drm/i915/i915_gem.c        |  8 ++++++++
 drivers/gpu/drm/i915/i915_gem_stolen.c | 14 ++++++++++++++
 drivers/gpu/drm/i915/intel_acpi.c      | 20 ++++++++++++++++++++
 4 files changed, 53 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 829b6f1..20d58ba 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1307,6 +1307,16 @@ struct i915_gem_mm {
 	 */
 	bool busy;
 
+	/**
+	 * Stolen will be lost upon hibernate (as the memory is unpowered).
+	 * Across resume, we expect stolen to be intact - however, it may
+	 * also be utililised by third parties (e.g. Intel RapidStart
+	 * Technology) and if so we have to assume that any data stored in
+	 * stolen across resume is lost and we set this flag to indicate that
+	 * the stolen memory is volatile.
+	 */
+	bool nonvolatile_stolen;
+
 	/* the indicator for dispatch video commands on two BSD rings */
 	int bsd_ring_dispatch_index;
 
@@ -3419,6 +3429,7 @@ intel_opregion_notify_adapter(struct drm_device *dev, pci_power_t state)
 #endif
 
 /* intel_acpi.c */
+bool intel_detect_acpi_rst(void);
 #ifdef CONFIG_ACPI
 extern void intel_register_dsm_handler(void);
 extern void intel_unregister_dsm_handler(void);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 77ac128..fd65d95 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -395,8 +395,16 @@ static struct drm_i915_gem_object *
 i915_gem_alloc_object_stolen(struct drm_device *dev, size_t size)
 {
 	struct drm_i915_gem_object *obj;
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	int ret;
 
+	if (!dev_priv->mm.nonvolatile_stolen) {
+		/* Stolen may be overwritten by external parties
+		 * so unsuitable for persistent user data.
+		 */
+		return ERR_PTR(-ENODEV);
+	}
+
 	mutex_lock(&dev->struct_mutex);
 	obj = i915_gem_object_create_stolen(dev, size);
 	if (IS_ERR(obj))
diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
index 335a1ef..4f44531 100644
--- a/drivers/gpu/drm/i915/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
@@ -482,6 +482,20 @@ int i915_gem_init_stolen(struct drm_device *dev)
 	 */
 	drm_mm_init(&dev_priv->mm.stolen, 0, dev_priv->gtt.stolen_usable_size);
 
+	/* If the stolen region can be modified behind our backs upon suspend,
+	 * then we cannot use it to store nonvolatile contents (i.e user data)
+	 * as it will be corrupted upon resume.
+	 */
+	dev_priv->mm.nonvolatile_stolen = true;
+#ifdef CONFIG_SUSPEND
+	if (intel_detect_acpi_rst()) {
+		/* BIOSes using RapidStart Technology have been reported
+		 * to overwrite stolen across S3, not just S4.
+		 */
+		dev_priv->mm.nonvolatile_stolen = false;
+	}
+#endif
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_acpi.c b/drivers/gpu/drm/i915/intel_acpi.c
index eb638a1..a827b31 100644
--- a/drivers/gpu/drm/i915/intel_acpi.c
+++ b/drivers/gpu/drm/i915/intel_acpi.c
@@ -23,6 +23,11 @@ static const u8 intel_dsm_guid[] = {
 	0x0f, 0x13, 0x17, 0xb0, 0x1c, 0x2c
 };
 
+static const struct acpi_device_id irst_ids[] = {
+	{"INT3392", 0},
+	{"", 0}
+};
+
 static char *intel_dsm_port_name(u8 id)
 {
 	switch (id) {
@@ -162,3 +167,18 @@ void intel_register_dsm_handler(void)
 void intel_unregister_dsm_handler(void)
 {
 }
+
+static int intel_match_device(struct device *dev, void* ids)
+{
+	if (acpi_match_device(irst_ids, dev))
+		return 1;
+
+	return 0;
+}
+bool intel_detect_acpi_rst(void)
+{
+	if (bus_for_each_dev(&acpi_bus_type, NULL, NULL, intel_match_device))
+		return true;;
+
+	return false;
+}
-- 
1.9.1